Conventional techniques for producing three-dimensional objects typically include assembling, machining, deforming, or casting. Assembly often involves gluing or welding individual components of moderate size together, while machining and deforming often involve removing material from or stressing the shape of preformed objects.
Casting, on the other hand, typically involves the injection of a liquid solution or polymer or a molten material into a mold. Casting is not, however, easily employed for manufacturing large objects or objects containing internal voids because polymerization and solidification are difficult to control within a mold. Casting is also a generally expensive method for generation of objects having custom shapes, especially for objects needed in small quantities.
U.S. Pat. No. 3,222,776 of Kawecki describes several embodiments for treating molten material. At column 6, lines 32-44 and in FIG. 5, Kawecki describes the ejection of droplets of molten material. Kawecki employs an ultrasonic generator to vibrate a discharge conduit at a predetermined frequency and amplitude in order to overcome the surface tension of the molten metal within the conduit. The resulting droplets harden while dropping from the end of the discharge conduit, are not discharged at the ultrasonic frequency but at an undetermined, inconsistent droplet discharge rate, and have uncontrolled trajectories and inconsistent diameter. This process is used only to create solid spheres of limited size and is not contemplated for building up free form structures in a controlled fashion.
At column 6, lines 45-55, and in FIG. 6, Kawecki describes an embodiment for ejecting a fine mist or spray 61 of molten material. Kawecki uses a mask or template to form objects because the mist or spray has a highly uncontrolled trajectory. This process vaguely resembles casting.
At column 6, lines 3-31, Kawecki describes an embodiment of his invention for extruding semisolid material in a continuous flow to create single filaments. The deposition rate of such a process is typically so high that it would cause slumping of a free form object deposited in layers. Although use of a very small orifice might reduce the slumping of the object due to high deposition rates, such a small orifice would tend to become plugged.
European patent application No. 90 311 640.8 of Crump describes a continuous flow delivery process now used commercially for viscous melts such as wax or plastic materials. Crump specifies that the delivery temperature of the material must be maintained close to its melting point (typically 1.degree. C. above its melting point). Use of a delivery temperature so close to the melting point would result in poor layer to layer bonding in materials such as metals. Crump also controls the distance of the ejection head from the substrate and employs the ejection head as a doctoring blade to limit the height or thickness of the layers of the viscous materials.
U.S. Pat. No. 4,655,492 of Masters, which is herein incorporated by reference, describes a method for constructing free-form objects from particulate matter in a manner that circumvents some of these problems. Masters directs individual particles of ceramic material to particular locations in a three-dimensional coordinate system and attaches the particles with adhesives to a seed point or previously deposited particles, gradually constructing an object of desired shape. Masters also describes the use of droplets of a water slurry containing ceramic particles which freezes upon impact with a seed point or previously deposited particles. The water is then presumably removed by lyophilization, creating a porous ceramic object. In either of these methods, the rate of deposition is independent of the type of particles used, and the time delay between deposition of the particles does not substantially affect the shape or solidity of the intended object.
The method of Masters would not, therefore, work well if it were applied to nonparticulate matter, such as materials in the liquid phase, especially those having well-defined solidification properties such as freezing points or polymerization initiators. In particular, Masters' slurry-droplet method would not work well for forming objects from molten salts, molten metals, or certain polymers. Such droplets take an irregular shape upon impact, and, if they freeze immediately, they retain that shape. The objects thus formed are typically irregular, weak, and porous.